The invention relates to a shift mechanism for a set of bicycle gears in accordance with the precharacterizing clause of claim 1.
European Patent Application EP 0 676 325 A2 has disclosed a twist grip shift for a bicycle, by means of which bicycle gears can be shifted using a Bowden line. The cable of the Bowden line is pulled into the housing of the shift mechanism by means of a cable reel when the latter is twisted in a winding rotational direction, a tensile force acting on the cable in the set of gears having to be overcome. The tensile force keeps the cable tensioned in the shift mechanism and in the Bowden line, for which reason the cable also rests on the cable reel when the cable reel is twisted in a releasing rotational direction, thereby releasing the cable in the direction of the bicycle gears. FIGS. 3, 5 and 6 show, in particular, the path of the cable from its fastening on the cable reel to the point where it leaves the housing, where there is no significant guidance of the cable associated with the redirection of the cable. When the cable reel is twisted in the winding rotational direction, jamming can namely occur in the bicycle gears, as a result of which the cable temporarily loses tension and, in the shift mechanism in particular, can cause a build-up on the cable reel between the point where the cable emerges from the housing and its end, this build-up causing the cable to spread out in an arc in the housing and rise from its proper position on the cable reel.
For the abovementioned case, the present invention provides guidance for the cable between the cable reel and the exit from the housing, preventing the cable from moving away to any significant extent from its position in the tensioned state when it is relaxed through delays in gear changes in the set of gears. Since the cable is generally secured on the cable reel by means of a nipple, it can furthermore also happen that when the cable is relaxed under the abovementioned conditions the nipple rises from its anchorage in the cable reel when the cable reel is rotated in the releasing rotational direction and causes jamming in the shift mechanism.
The invention has thus set itself the object of guiding a Bowden cable, which can be subjected essentially only to tension, in such a way on its way between its fastening on a cable reel by means of a nipple and the point where it emerges from a housing part of the shift mechanism that, when the cable reel is operated in the releasing rotational direction, the cable does not move away from the position it occupies under tensile loading, especially when the nipple is firmly connected to the cable reel.
This object is achieved by the features in the characterizing part of claim 1. Refinements can be found in the subclaims. An exemplary embodiment of a cable guide in a shift mechanism for bicycle gears is explained with reference to two partial sections, in which: